The present invention relates generally to a control system for a chiller unit, and more specifically, to a control system for a steam turbine powered chiller unit that integrates the control operations of both the steam turbine system and the chiller unit.
While most heating, ventilation and air conditioning (HVAC), refrigeration, or chiller systems use electric motors to power the corresponding compressor(s) in the chiller system, some chiller systems can use a steam turbine to power the compressor. Typically, these steam turbine powered chiller systems have required an excessive amount of fieldwork to install and connect the chiller system to the steam turbine system. Some previous steam turbine driven chiller units or systems have involved the packaging of the steam turbine on the chiller unit and resulted in unique installations requiring field routed piping and instrumentation to link the steam turbine system with the chiller unit to complete the installation.
In these previous steam turbine driven chillers systems, many of the controls used with the steam turbine and the chiller unit, e.g., steam turbine governor control, pre-rotation vane control, hot gas control, turbine torque limitation control and surge prevention control, were “stand alone” controls that operated independently of the other controls and did not communicate with the other controls. For example, a turbine speed control could operate substantially independently from a pre-rotation vane control and both the turbine speed control and the pre-rotation vane control could operate substantially independently of a hot gas bypass valve control. This independent operation of controls often resulted in inefficiencies in the operation of the steam turbine driven chiller system, as one control operation on one part of the system would remove or limit the efficiency gained from another control operation on another part of the system. In addition to losses in efficiency, the use of independent controls also limited effective surge prevention in the compressor of the chiller system because the separate systems were not able to measure or monitor the system pressure differential (condenser pressure minus evaporator pressure).
Therefore, what is needed is a control system for a steam turbine powered chiller unit that can integrate into a single control panel both the controls for the steam turbine and the controls for the chiller unit, while maximizing the efficiency of operation of both the steam turbine and the chiller unit.